Abstract
In this study, we reported a silver sinusoidal nanograting used in microchannels, forming H2O/Ag/NOA/SiO2 heterostructure and studied the impact of interactions of grating-coupled surface plasmon polaritons (SPPs) on surface-enhanced Raman scattering (SERS). There are two modes of \(E_{x} (z)\) in the Ag grating, namely, the anti-symmetric mode (AM) at the high SPP resonance frequency and the symmetric mode (SM) at the low-SPP resonance frequency. When the refractive indices of the upper and lower dielectrics of the thin Ag grating are close, there will be a strong coupling between the SPPs of the two interfaces, which will increase the transmittance but reduce the maximum electromagnetic (EM) of the SERS substrate. Additionally, the thinner the Ag grating, the stronger the coupling, accompanied by the frequency shift of the two coupling modes. Our experimental results are supported by FDTD calculations, which have corroborated the importance of the interactions of grating-coupled SPPs in the design of SERS substrate.
Highlights
Nanostructures that support surface plasmon resonance (SPR) have been widely used for sensing applications through the use of different techniques, including SPR spectroscopy[1, 2], SPR imaging[3] and surface-enhanced Raman scattering (SERS) spectroscopy[4,5,6,7]
We report on the optical study of coupling modes of surface Plasmon polaritons (SPPs) supported by silver sinusoidal nanograting deposited on a Norland Optical Adhesive (NOA) coated glass substrate used in microchannels, forming a H2O/Ag/NOA heterostructure
It can be seen that a strong coupling of SPPs occurs at 773nm and 813nm respectively, corresponding to the two resonance wavelengths, where the reflectance curve shows two sharp troughs, while two sharp peaks appear in the corresponding transmittance and absorbance curves
Summary
Nanostructures that support surface plasmon resonance (SPR) have been widely used for sensing applications through the use of different techniques, including SPR spectroscopy[1, 2], SPR imaging[3] and surface-enhanced Raman scattering (SERS) spectroscopy[4,5,6,7]. Metallic nano-gratings[16, 17], in particular, experience large-area uniform electromagnetic enhancement[18, 19], which increases the chances for analyte detection via SERS spectroscopy[19,20,21]. Their properties are connected to surface plasmon polariton (SPP), whose resonance wavelength depends on the geometrical parameters of the nanograting, the incident light and the surrounding medium[7]. We estimated the impact of interaction of grating-coupled SPPs on the SERS, by varying the thickness of Ag grating, the refractive index of the surrounding medium of the superstrate and substrate. They confirm the importance and the impact of interactions of gratingcoupled SPPs in the design of SERS substrates by considering the appropriate grating constant in accordance with FDTD simulations
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